How would it cost to have you guys replace 2 violin strings

Reasonable

Not that much. You can go and check it out.

It would cost about $15/16 for new strings (we only have packs of four, not single strings for violin), and about $5 or $10 for labor (as long as nothing else is wrong). It's free for our techs to look at any instrument, evaluate what it might need, and give you an estimate on the work, before you drop it off.